Xenix

BSD

Barkeley Software Distribution, also called Berkeley Unix. Today the term “BSD” is used to refer to any of the BSD descendants(后代) which together form a branch of the family of Unix-like OS.(共同组成了一个分支)

FreeBSD & Apple

NeXTSTEP

An object-oriented, multitasking OS. Low-level C but High-level OC language and runtime the first time, combined with an OO aplication layer and including several “kits”.
大家都知道 NeXT 是 Steve Jobs 被 forced out of Apple 后和 a few of his coworkers 创办的，所以 NeXTSTEP 绝对是证明 Jobs 实力的作品。

Darwin

Darwin, the core set of components upon which Mac OS X and iOS based, mostly POSIX compatible, but has never, by itself, been certified as being compatible with any version of POSIX. (OS X, since Leopard, has been certified as compatible with the Single UNIX Specification version 3)所以说 Mac OS X 算是很正统 Unix 的了

POSIX

可移植操作系统接口, Portable Operating System Interface, is a family of standards specified by the IEEE from maintaining compatibility between OS, defines the API along with Command Line Shells and utility interfaces, for software comaptibility with variants of Unix and other OS.

Fully POSIX compliant:

OS X

QNX OS (BlackBerry)

Mostly complicant:

Linux

OpenBSD/FreeBSD

Darwin (Core of iOS & OS X)

Android

Complicant via compatibility feature （通过兼容功能实现兼容）

Windows NT Kernel

Windows Server 2000, 2003, 2008, 2008 R2, 2012

Symbian OS (with PIPS)

Symbian was a closed-source OS.

Unix-like

A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification.

There is no standard for defining the term.
其实 Unix-like 是个相对模糊的概念：

最狭义的 Unix 单指 Bell Labs’s Unix

稍广义的 Unix 指代所有 Licensed Unix, 即通过了 SUS 的 Unix-like ，比如 OS X

最广义的 Unix 即所有 Unix-like 系统，无论它是否通过过任何 SUS，包括 Linux，BSD Family 等

Single UNIX Specification

The Single UNIX Specification (SUS) is the collective name of a family of standards for computer OS, compliance with which is required to qualify for the name “Unix”, like POSIX.

Apple iOS

iOS is a Unix-like OS based on Darwin(BSD) and OS X, which share some frameworks including Core Foundation, Founadtion and the Darwin foundation with OS X, but, Unix-like shell access is not avaliable for users and restricted for apps, making iOS not fully Unix-compatible either.

The iOS kernal is XNU, the kernal of Darwin.

XNU Kernel

XNU, the acronym(首字母缩写) for X is Not Unix, which is the Computer OS Kernel developed at Apple Inc since Dec 1996 for use in the Mac OS X and released as free open source software as part of Darwin.

In order to ensure that the entire software of a computer grants its users all freedom rights (use, share, study, modify), even the most fundamental and important part, the operating system, needed to be written.

This OS is decided to called GNU (a recursive acronym meaning “GNU is not Unix”). By 1992, the GNU Project had completed all of the major OS components except for their kernel, GNU Hurd.

With the release of the third-party Linux Kernel, started independently by Linus Torvalds in 1991 and released under the GPLv0.12 in 1992, for the first time it was possible to run an OS composed completely of free software.

Though the Linux kernel is not part of the GNU project, it was developed using GCC and other GNU programming tools and was released as free software under the GPL.

Android

Android is a mobile OS based on Linux Kernel, so it’s definitely Unix-like.

Linux is under GPL so Android has to be open source.
Android’s source code is released by Google under open source licenses, although most Android devices ultimately ship with a combination of open source and proprietary software, including proprietary software developed and licensed by Google (GMS are all proprietary)

Android Kernel

Android’s kernel is based on one of the Linux kernel’s long-term support (LTS) branches.

Android’s variant of the Linux kernel has further architectural changes that are implemented by Google outside the typical Linux kernel development cycle, and, certain features that Google contributed back to the Linux kernel. Google maintains a public code repo that contains their experimental work to re-base Android off the latest stable Linux versions.

Android ROM

既然提到 Android 就不得不提提 Android ROM

ROM 的本义实际上是只读内存：

Read-only memory (ROM) is a class of storage medium used in computers and other electronic devices. Data stored in ROM can only be modified slowly, with difficulty, or not at all, so it is mainly used to distribute firmware (固件) (software that is very closely tied to specific hardware, and unlikely to need frequent updates).

A custom firmware, also known as a custom ROM, ROM, or custom OS, is an aftermarket distribution of the Android operating system. They are based on the Android Open Source Project (AOSP), hence most are open-sourced releases, unlike proprietary modifications by device manufacturers.